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Cuttings of the southeast Asian tropical rain forest tree species, Pongamia pinnata (L.) Pierre were raised in growth chambers providing a photosynthetic photon flux density (PPFD) of 60 μmol m−2 s−1 with either a low or a high red:far-red light ratio (LR and HR, repectively). The chambers were supplied with air containing CO2 at a concentration of either 400 (LR4 and HR4, respectively) or 800 μmol mol−1 (HR8 and LR8, respectively). After 4 months, leaf morphology and photosynthetic characteristics were determined. Relative to HR4, the LR4 treatment increased leaf area and total chlorophyll concentration (Chl) by 24 and 25%, respectively, but reduced leaf mass per unit area (LMA) by 19%. Elevated [CO2] significantly increased leaf area and LMA but did not affect Chl of LR or HR plants. Leaf nitrogen concentration was unaffected by the red:far-red light ratio but decreased significantly in seedlings in the elevated [CO2] treatment. Photosynthesis measured in situ under the growth conditions of ambient light and [CO2] (Aamb) was 30% lower on an area basis and 14% lower on a mass basis in LR4 plants than in HR4 plants. Elevated [CO2] reduced the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and thus decreased light-saturated photosynthetic rate in both HR and LR plants. Elevated [CO2] increased mean leaf area and decreased respiration rates in both LR and HR plants. The LR8 plants had significantly higher Aamb than LR4 plants, but similar Aamb to HR8 plants. [ABSTRACT FROM PUBLISHER]